Canned pump

ABSTRACT

In a magnet pump in which a cylinder  4 A integrated with a drive shaft  3 A and provided with a drive magnet M 1  on the inner circumferential side thereof is disposed outside a cylindrical can  2 A having a bottom and secured to a pump casing  1 A, and a rotor  6 A concentrically fitted over an impeller shaft  5 A and provided with a driven magnet M 2  on the outer circumferential side thereof is disposed inside the can  2 A, and the rotor  6 A rotates integrally with an impeller  7 A around the impeller shaft  5 A as the drive shaft  3 A rotates, by virtue of a magnetic attraction force generated between the drive magnet M 1  and the driven magnet M 2 , wherein the sliding contact members of the pump, a bushing  81 , a sleeve  82  and a thrust ring  83  interposed in each of the bearing sections  8   f A and  8   r A for the impeller shaft  5 A, are made of ceramic or cemented carbide and have a diamond-like carbon film.

FIELD OF THE INVENTION

The invention pertains to the field of canned pumps, and in particular to canned magnetic pumps.

BACKGROUND OF THE INVENTION AND STATEMENT OF RELATED ART

The present invention relates to a canned pump, such as a canned magnetic coupling type magnet pump and a canned motor pump, wherein an impeller shaft and the bearing sections thereof are disposed inside a can, and a rotor fitted over the impeller shaft rotates integrally with an impeller by virtue of the magnetic action between the inside and outside of the can.

Generally speaking, in a canned magnetic coupling type magnet pump, a cylinder integrated with a drive shaft and having a drive magnet on the inner circumferential side thereof is disposed outside a cylindrical can having a bottom, the inside of the can being communicated with the inside of the pump, and a rotor concentrically fitted over an impeller shaft and having a driven magnet on the outer circumferential side thereof is disposed inside the can. The rotor rotates integrally with an impeller installed at the front end of the impeller shaft as the drive shaft rotates, by virtue of a magnetic attraction force generated between the two magnets, thereby carrying out a pumping action. Furthermore, in a canned motor pump, a motor stator is disposed outside a can of a similar kind, and a motor rotor concentrically fitted over an impeller shaft is disposed inside the can. As electric power is supplied to the stator, the rotor rotates integrally with an impeller in a similar way, thereby carrying out a pumping action.

Hence, in these canned pumps, since the impeller shaft and the rotor, including the bearing sections, are disposed inside the can and have no shaft sealing section between the inside and the outside, there is no leakage of liquid, and internal contamination owing to the entry of microorganisms from the outside does not occur. Therefore, the canned pumps are suited to transfer liquids having risks, such as corrosivity, toxicity, flammability and radioactivity, and liquids requiring advanced hygienic supervision, such as drinkable water, fruit juice, liquor, or seasoning liquid.

However, in such a canned pump, no lubricating oil can be used at the bearing sections for the impeller shaft because of its structure. Hence, generally speaking, components made of a ceramic material being high in hardness and excellent in abrasion resistance are used as sliding contact members interposed in the bearing sections, and furthermore, part of the working liquid is circulated inside the can so as to pass through the clearance between the can and the rotor, the clearance between the rotor and the impeller shaft or the inside of the impeller shaft to prevent the bearing sections from being broken and to suppress the bearing sections from being worn, by virtue of the lubrication action of the liquid being interposed, and to cool the bearing sections being heated by friction and the can being heated by resistance due to an eddy current. This prevents malfunction owing to thermal degradation of the liquid and thermal demagnetization in the magnet pump (for example, Patent Documents 1 to 4).

[Patent Document 1] Japanese Published Unexamined Patent Application No. S58-13349

[Patent Document 2] Japanese Published Unexamined Patent Application No. S58-138294

[Patent Document 3] Japanese Published Unexamined Patent Application No. S61-164098

[Patent Document 4] Japanese Published Unexamined Utility Model Application No. S61-122393

However, such a conventional canned pump falls into the so-called dry operation state wherein the impeller is rotated while no liquid is distributed to the inside of the can, owing to an operating error or the like when liquid feeding is started or when liquid feeding is resumed after operation interruption. As a result, the bearing sections for the impeller shaft are broken shortly after the start of operation, and liquid feeding is frequently made impossible. Furthermore, the working liquid becomes a gas-liquid mixture state owing to improper air venting in the previous stage or because of air bubbles generated from the liquid, and the bearing sections for the impeller shaft fall into a dry sliding contact state intermittently and are worn, whereby the sliding contact members are frequently forced to be replaced at an early stage.

SUMMARY OF THE INVENTION

In consideration of the above-mentioned circumstances, the present invention is intended to provide a canned pump wherein the bearing sections for the impeller shaft are prevented from being broken and suppressed from being worn even if a dry operation state occurs or the working liquid becomes a gas-liquid mixture state temporarily, thereby being capable of being excellent in durability and low in maintenance cost.

For the purpose of attaining the above-mentioned object, in a canned pump constructed according to the present invention, the sliding contact members interposed in the bearing sections for the impeller shaft have a diamond-like carbon (DLC) film on the sliding contact faces thereof. Since this DLC film is extremely hard, has a very low friction coefficient and is excellent in the adhesion strength to the base material thereof, such as ceramic or cemented carbide, the sliding torque at the sliding contact face therebetween is reduced to a small value even if a dry operation state occurs temporarily because of an operating error or the like at the start of liquid feeding or at the time when liquid feeding is resumed after operation interruption. Hence, breakage owing to load impact is prevented, and abrasion hardly occurs. Furthermore, even if the sliding contact members having been heated by frictional heat generation are quickly chilled by supplying liquid without allowing a sufficient time after dry operation, separation and cracks owing to heat shock do not occur, whereby subsequent liquid feeding can be carried out in a proper state. On the other hand, even in the case where the working liquid becomes a gas-liquid mixture state owing to improper air venting in the previous stage or because of air bubbles generated from the liquid, the sliding contact members are not broken and are suppressed from being worn, and normal operation can be resumed thereafter, and liquid feeding can be carried out without problems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical sectional side view showing a magnet pump in accordance with a first embodiment of the present invention;

FIG. 2 is an enlarged vertical sectional side view showing the main sections of the magnet pump shown in FIG. 1;

FIG. 3 is a perspective view showing a bushing used in the magnet pump shown in FIG. 1;

FIG. 4 is a vertical sectional side view showing a magnet pump in accordance with a second embodiment of the present invention;

FIG. 5 is a vertical sectional side view showing a canned motor pump in accordance with a third embodiment of the present invention; and

FIG. 6 is a schematic view showing a principle of forming a diamond-like carbon film using the plasma ion implantation method conforming to the radio-frequency high-voltage pulse superimposition system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

Canned magnetic coupling type magnet pumps in accordance with the first and second embodiments of the present invention and a canned motor pump in accordance with a third embodiment of the present invention, serving as canned pumps in accordance with the present invention, will be described below specifically referring to the drawings.

As shown in FIG. 1 and FIG. 2, the casing 1A of a magnet pump P1 in accordance with the first embodiment comprises a front casing member 11 equipped with a liquid suction port 11 a and a liquid delivery port 11 b, a cylindrical intermediate casing member 12 connected to this front casing member 11 at the front end flange section 12 a thereof via a ring-shaped flange member 14 and bolts 15 a, and 15 b, and a cylindrical rear casing member 13 connected to the rear end flange section 12 b of this intermediate casing member 12 at the front end flange section 13 a thereof via bolts 15 c. The inside of the casing 1A is divided into a pump chamber 1 a on the side of the front casing member 11 and a magnetic coupling chamber 1 b on the side of the intermediate casing member 12 by a partition plate 16 interposed between the front casing member 11 and the intermediate casing member 12. Furthermore, a pump drive section comprising a motor, not shown, is provided on the side of the rear casing member 13.

At the central section inside the casing 1A, an impeller shaft 5A extending in the back and forth direction passes through the partition plate 16 and is disposed between the pump chamber 1 a and the magnetic coupling chamber 1 b. An impeller 7A disposed inside the pump chamber 1 a is installed at the front end of this impeller shaft 5A via an impeller nut 7 a and an engagement key 5 a so as not to be rotatable mutually. In addition, inside the magnetic coupling chamber 1 b, the front end flange section 2 b of a cylindrical can 2A having a thick bottom section 2 a directed rearward is disposed between the front casing member 11 and the ring-shaped flange member 14, and the front end flange section 2 b is secured to the partition plate 16 using bolts 15 d, whereby the cylindrical can 2A is disposed concentrically with the impeller shaft 5A. Furthermore, the front end section of the impeller shaft 5A is rotatably supported on the boss section 16 a of the partition plate 16 via a front bearing section 8 fA, and the rear end section thereof is also rotatably supported on the bearing hole section 2 c of the bottom section 2 a of the can 2A via a rear bearing section 8 rA.

The inside of the magnetic coupling chamber 1 b is divided by the can 2A into a drive-side space 10 a on the outside and a driven-side space 10 b on the inside so as to be liquid-tight. The driven-side space 10 b is communicated with the pump chamber 1 a via through holes 16 b formed on the partition plate 16. Furthermore, a drive shaft 3A enters the drive-side space 10 a from the rear side so as to be concentric with the impeller shaft 5A. A cup-shaped cylinder 4A being open forward is secured to this drive shaft 3A at the rear end boss section 4 a thereof via an engagement key 3 a and a set screw 3 b. Hence, this cylinder 4A is fitted over the can 2A while having a small clearance 9 a between a drive magnet M1 provided as a drive magnetic force generating means on the inner circumference of the cylinder 4A and the outer circumferential face of the can 2A. On the other hand, in the driven-side space 10 b, a rotor 6A fitted over the impeller shaft 5A via an engagement key 5 b so as not to be rotatable mutually is disposed while having a small clearance 9 b between the outer circumferential face of the rotor 6A in which a driven magnet M2 is embedded and the inner circumferential face of the can 2A.

Each of the front and rear bearing sections 8 fA and 8 rA comprises three sliding contact members, that is, a bushing 81 engaged with the bearing hole section 16 c inside the boss section 16 a of the partition plate 16 serving as the stationary side and the bearing hole section 2 c of the can 2A via an engagement pin 17 a so as not to be rotatable mutually, a sleeve 82 fitted over the impeller shaft 5A serving as the rotating side via the engagement key 5 b so as not to be rotatable mutually, and a thrust ring 83. Furthermore, the sleeve 82 is disposed inside the bushing 81, and the thrust ring 83 is fitted into the ring-shaped concave section 6 a of the rotor 6A at the central side of the end face thereof and disposed so as to make sliding contact with the end face of the bushing 81.

In addition, as also shown in FIG. 3, multiple (four in the figure) liquid-flowing grooves 81 a extending in the axial direction are formed on the inner circumferential face making sliding contact with the outer circumferential face of the sleeve 82 so as to be equally distributed in the circumferential direction. Furthermore, multiple liquid-flowing grooves 81 b, extending in the radial direction and connected to the respective liquid-flowing grooves 81 a formed on the inner circumferential face, are also formed on the end face making sliding contact with the thrust ring 83 so as to be equally distributed in the circumferential direction. Numeral 81 c in FIG. 3 designates an engagement groove engaged with the engagement pin 17 a (see FIG. 2).

The three sliding contact members, the bushing 81, the sleeve 82 and the thrust ring 83, of each of these bearing sections 8 fA and 8 rA are molded products made of ceramic, such as silicon carbide (SiC), or cemented carbide, such as tungsten carbide (WC), the entire surface of each being coated with a DLC film (diamond-like carbon film). The can 2A and the impeller shaft 5A are made of stainless steel, such as SUS316.

On the other hand, the impeller shaft 5A and the impeller nut 7 a screwed at the front end thereof are provided with a liquid-flowing hole 21 passing through the entire length along the axial centers of the two. In addition, a liquid reservoir section 22 is provided between the rear end of the impeller shaft 5A and the bearing hole section 2 c of the can 2A, and the liquid reservoir section 22 is communicated with the pump chamber 1 a via the liquid-flowing hole 21. Furthermore, the ring-shaped sliding contact portion between the inner circumference of the bushing 81 and the outer circumference of the sleeve 82 in the rear bearing section 8 rA faces the liquid reservoir section 22 on the rear end side. Moreover, in the front bearing section 8 fA, a liquid-flowing clearance 23 is formed between the shaft insertion hole 16 d of the partition plate 16 and the impeller 7A, and the ring-shaped sliding contact portion between the inner circumference of the bushing 81 and the outer circumference of the sleeve 82 faces the liquid-flowing clearance 23 on the front end side. Still further, the sliding contact portion between the bushing 81 and the sleeve 82 in each of the two bearing sections 8 fA and 8 rA faces the driven-side space 10 b on the outer circumferential side.

In this magnet pump P1 in accordance with this first embodiment, when the cylinder 4A is rotated by driving the drive shaft 3A, the rotor 6A is driven and rotated integrally with the impeller shaft 5A by virtue of a magnetic attraction force generated between the drive magnet M1 and the driven magnet M2. Hence, the working liquid to be fed is sucked through the liquid suction port 11 a and pressure-fed from the liquid delivery port 11 b to a target region by virtue of the centrifugal pump action owing to the rotation of the impeller 7A integrated with the impeller shaft 5A.

In the normal operation state of this magnet pump P1, the driven-side space 10 b is entirely filled with the working liquid through the through holes 16 b of the partition plate 16 and the small clearance 9 b. In addition, in the front bearing section 8 fA, the working liquid having entered the driven-side space 10 b from the pump chamber 1 a through the through holes 16 b penetrates into the liquid-flowing grooves 81 b of the bushing 81 from the outside, and is distributed to the entire sliding contact portion between the bushing 81 and the thrust ring 83. Furthermore, the working liquid penetrates into the liquid-flowing grooves 81 a of the bushing 81 and is distributed to the sliding contact portion between the bushing 81 and the sleeve 82. Still further, the working liquid passes through the liquid-flowing clearance 23 and returns to the pump chamber 1 a to join the working liquid inside the pump chamber 1 a, and is delivered by the impeller 7A. Also, in the rear bearing section 8 rA, the working liquid having entered the driven-side space 10 b from the pump chamber 1 a through the through holes 16 b penetrates into the liquid-flowing grooves 81 b of the bushing 81 from the outside through the small clearance 9 b on the peripheral side, and is distributed to the entire sliding contact portion between the bushing 81 and the thrust ring 83. Furthermore, the working liquid penetrates into the liquid-flowing grooves 81 a of the bushing 81 and is distributed to the sliding contact portion between the bushing 81 and the sleeve 82, enters the liquid reservoir section 22, passes from the liquid reservoir section 22 through the liquid-flowing hole 21 and returns to the pump chamber 1 a. Hence, in the two bearing sections 8 fA and 8 rA, the sliding contact members (81 to 83) make sliding contact with one another while the working liquid is interposed. The lubricating action of the interposed liquid prevents breakage of the sliding contact members (81 to 83) and suppresses abrasion of the sliding contact members. Additionally, the temperature rise owing to heat generation due to the friction at the sliding contact portions and owing to heat generation due to the resistance at the can 2A is avoided by the cooling action obtained by heat exchange with the working liquid.

On the other hand, in the case where the pump falls into a dry operation state wherein the pump is operated while no liquid is fully distributed to the driven-side space 10 b because of negligence in not supplying priming water at the start of liquid feeding or because of an operating error, such as negligence in not checking the liquid level inside the pump at the time when liquid feeding is resumed after operation interruption, the sliding contact members (81 to 83) of each of the two bearing sections 8 fA and 8 rA make sliding contact with one another in a dry operation state without the lubricating action of the liquid. However, the bushing 81, the sleeve 82 and the thrust ring 83 serving as the sliding contact members of each of the two bearing sections 8 fA and 8 rA are molded products made of silicon carbide, the entire surface of each being coated with a DLC film. Since this DLC film is extremely hard and has a very low friction coefficient, the sliding torque at the sliding contact face therebetween is reduced to a small value even when the dry operation state continues for a certain period of time. Hence, breakage owing to load impact is prevented, and abrasion hardly occurs, whereby subsequent normal operation can be carried out without problems. Furthermore, even if the sliding contact members (81 to 83) having been heated by frictional heat generation are quickly chilled by supplying liquid without allowing a sufficient time after dry operation, fissures and cracks owing to heat shock do not occur, whereby subsequent liquid feeding can be carried out in a proper state.

Furthermore, in the case where the working liquid becomes a gas-liquid mixture state owing to improper air venting in the previous stage or because of air bubbles generated from the liquid, the bubbles enter the sliding contact portions of the sliding contact members (81 to 83), and the two bearing sections 8 fA and 8 rA fall into a dry sliding contact state intermittently. However, even in this case, since the sliding contact surfaces of the sliding contact members (81 to 83) are coated with the DLC film being extremely hard and having a very low friction coefficient, and since the DLC film firmly adheres to the base material of the sliding contact members, such as ceramic or cemented carbide, abrasion hardly occurs between the surfaces. Hence, after resuming normal operation thereafter, liquid feeding can be carried out without problems. Furthermore, even if a gas-liquid mixture state occurs frequently according to the type of the working liquid, abrasion is suppressed to a slight degree, whereby the sliding contact members can be used continuously for a long time.

The fact that the pump has fallen into the above-mentioned dry operation state or gas-liquid mixture operation state can be indicated by insufficient discharge pressure, stop or fluctuation of liquid flow, abnormal decrease in current value, etc.

The casing 1B of a magnet pump P2 in accordance with a second embodiment shown in FIG. 4 comprises a front casing member 31 equipped with a liquid suction port 31 a and a liquid delivery port 31 b, a cylindrical intermediate casing member 32 connected to this front casing member 31 at the front end flange section 32 a thereof via bolts 15 e, and a cylindrical rear casing member 33 connected to the rear end flange section 32 b of this intermediate casing member 32 at the front end flange section 33 a thereof via bolts 15 f. In addition, inside the casing 1B, the front end flange section 2 e of a cylindrical can 2B having a bottom is held between the opposed end faces of the front casing member 31 and the intermediate casing member 32, whereby the cylindrical can 2B is disposed with the bottom section 2 f directed rearward. Furthermore, the inside of the casing 1B is divided by this can 2B into a drive-side space 20 a on the outside of the can 2B and a driven-side space 20 b extending from the inside of the can 2B to a pump chamber 30 on the side of the front casing member 31. A pump drive section comprising a motor, not shown, is provided on the side of the rear casing member 33.

A drive shaft 3B enters the drive-side space 20 a from the rear side so as to be concentric with the can 2B. A cup-shaped cylinder 4B, the rear end boss 4 b of which is secured to this drive shaft 3B via a keyway 3 c and a set screw 3 d, is disposed so as to have a small clearance 9 c between a drive magnet M1 provided as a drive magnetic force generating means on the inner circumference of the cylinder 4B and the outer circumference of the can 2B.

On the other hand, in the driven-side space 20 b, an impeller shaft 5B extending along the center line of the can 2B is held so as to be unrotatable since its front end section 5 c having a partially cut circular cross-section is fitted into a boss section 31 c formed integrally with the front casing member 31 and its rear end section 5 d is fitted into a boss section 2 g formed at the center of the inner face side of the bottom section 2 f of the can 2B. Hence, a rotor 6B rotatably fitted over the impeller shaft 5B via front and rear bearing sections 8 fB and 8 rB is disposed inside the can 2B while having a small clearance 9 d between the outer circumferential face of the rotor 6B in which a driven magnet M2 is embedded and the inner circumferential face of the can 2B. Furthermore, an impeller 7B integrally installed at the front end of the rotor 6B is disposed inside the pump chamber 30.

The front bearing section 8 fB comprises two sliding contact members, that is, a bushing 84 fitted into the ring-shaped concave section 6 b at the central side of the front end face of the rotor 6B and engaged with the rotor 6B via an engagement pin 17 b, and thrust ring 85 unrotatably fitted over the front end section 5 a of the impeller shaft 5B, the front end section 5 a having a partially cut circular cross-section. The inner circumferential face of the bushing 84 makes sliding contact with the outer circumferential face of the impeller shaft 5B, and the front end face of the bushing 84 makes sliding contact with the rear end face of the thrust ring 85. Furthermore, in the rear bearing section 8 rB, only the bushing 84 fitted over and engaged with the rear end side of the rotor 6B as in the front end side is used as a sliding contact member, and the inner circumferential face of the bushing 84 makes sliding contact with the outer circumferential face of the impeller shaft 5B. As in the bushing 81 in accordance with the first embodiment, multiple liquid-flowing grooves 84 a extending in the axial direction are formed on the inner circumferential face of the bushing 84 so as to be equally distributed. Furthermore, multiple liquid-flowing grooves 84 b, extending in the radial direction and connected to the respective liquid-flowing grooves 84 a, are also formed on the outer end face so as to be equally distributed.

Hence, like the sliding contact members (81 to 83) of each of the bearing sections 8 fA and 8 rA in accordance with the first embodiment, the bushing 84 and the thrust ring 85 serving as the sliding contact members of each of the two bearing sections 8 fB and 8 rB are molded products made of ceramic, such as silicon carbide (SiC), or cemented carbide, such as tungsten carbide (WC), the entire surface of each being coated with a DLC film. Furthermore, the impeller shaft 5B is a molded product made of ceramic, such as silicon carbide since it makes sliding contact with the bushings 84 at the front and rear bearing sections 8 fB and 8 rB.

This magnet pump P2 in accordance with the second embodiment is an impeller shaft fixture type. When the cylinder 4B is rotated by driving the drive shaft 3B, the rotor 6B is driven and rotated integrally with the impeller 7B around the impeller shaft 5B by virtue of a magnetic attraction force generated between the drive magnet M1 and the driven magnet M2. Hence, the working liquid to be fed is sucked through the liquid suction port 31 a and pressure-fed from the liquid delivery port 31 b to a target region by virtue of the centrifugal pump action owing to the rotation of this impeller 7B. In the normal operation state of this pump, the driven side space 20 b is entirely filled with the working liquid. Part of the working liquid in the pump chamber flows toward the central side of the driven-side space 20 b through the small clearance 9 d, penetrates into the liquid-flowing grooves 84 a, on the inner circumference of the bushing 84 through the liquid-flowing grooves 84 b, on the outer end face of the bushing 84 of the rear bearing section 8 rB and is distributed to the portion making sliding contact with the impeller shaft 5B. Furthermore, the liquid flows forward through the ring-shaped space between the impeller shaft 5B and the rotor 6B, penetrates into the liquid-flowing grooves 84 a on the inner circumference of the bushing 84 of the front bearing section 8 fB and is distributed to the portion making sliding contact with the impeller shaft 5B. Then, the liquid penetrates into the liquid-flowing grooves 84 b on the outer end face of the bushing 84 and is distributed to the sliding contact portion between the bushing 84 and the thrust ring 85. Still further, the liquid passes through the space between the outer circumference of the thrust ring 85 and the inner circumference of the base section of the impeller 7B and returns to the pump chamber 30, and is delivered together with the working liquid inside the pump chamber 30 by the impeller 7B. Therefore, the working liquid is interposed in the sliding contact portions of the two bearing sections 8 fB and 8 rB, and the smooth rotation of the impeller 7B is ensured by the lubricating action of the liquid. Hence, the sliding contact members (84 and 95) are prevented from being broken, and the sliding contact members (84 and 95) and the surface of the impeller 7B making sliding contact with these sliding contact members are suppressed from being worn. Moreover, the temperature rise owing to heat generation due to the friction at the sliding contact portions and owing to heat generation due to the resistance of the can 2B is avoided by the cooling action obtained by heat exchange with the working liquid.

On the other hand, even in the case where the pump falls into a dry operation state wherein the pump is operated while no liquid is fully distributed to the driven-side space 20 b because of negligence in not supplying priming water at the start of liquid feeding or because of an operating error, such as negligence in not checking the liquid level inside the pump at the time when liquid feeding is resumed after operation interruption, or in the case where the working liquid becomes a gas-liquid mixture state owing to improper air venting in the previous stage or because of air bubbles generated from the liquid, since the surfaces of the sliding contact members, that is, the bushing 84 and the thrust ring 85, are coated with a DLC film being extremely hard and having a very low friction coefficient and since the adhesion strength of the DLC film to the ceramic or cemented carbide material serving as the base material of the sliding contact members is excellent, as in the above-mentioned first embodiment, the sliding torque at the sliding contact face therebetween is reduced to a small value. Hence, breakage owing to load impact is prevented, and abrasion hardly occurs. Liquid feeding can thus be carried out without problems by resuming normal operation after the detection of abnormality. Furthermore, even if the liquid is supplied without allowing a sufficient time after dry operation, film separation and cracks owing to heat shock do not occur.

The casing 1C of a canned motor pump P3 in accordance with a third embodiment shown in FIG. 5 comprises a front casing member 51 equipped with a liquid suction port 51 a and a liquid delivery port 51 b, a partition plate 52 connected to this front casing member 51 at the peripheral portion thereof via bolts 15 g, a nearly cylindrical rear casing member 53 connected to this intermediate partition plate 52 at the front end flange section 53 a thereof via bolts 15 h, a rear end plate 54 connected to the rear end of this rear casing member 53 at the peripheral section thereof via bolts 15 i, and a support base 55 connected to the lower section of the rear casing member 53 via bolts 15 j.

In addition, the rear casing member 53 and the rear end plate 54 constitute a cylindrical can 2C having a bottom, and the inside of this can 2C serves as a rotor chamber 60. At the central section inside the rotor chamber 60, an impeller shaft 5C journaled on the partition plate 52 and the rear end plate 54 via front and rear bearing sections 8 fC and 8 rC is disposed. A coil section 61 wound around this impeller shaft 5C and a stainless steel cover section 62 are used to form a rotor 6C. Furthermore, the front end section of the impeller shaft 5C passes through the partition plate 52 and enters a pump chamber 50. An impeller 7C is installed on this front end section via an impeller nut 7 b and an engagement key 5 e so as to be unrotatable mutually. On the other hand, inside the peripheral wall section 53 b of the rear casing member 53, stator pits 40 separated from the rotor chamber 60 by a thin inner wall section 53 c are formed at multiple positions in the circumferential direction. A stator 4C comprising a core section 41 serving as a motor driving magnetic force generating means and a coil section 42 is disposed in each stator pit 40. The stainless steel cover section 62 of the rotor 6C is disposed so as to have a small clearance 9 e between the outer circumferential face thereof and the inner circumferential face of the can 2C.

The rotor chamber 60 is communicated with the pump chamber 50 via through holes 24, formed on the peripheral side of the partition plate 52. In addition, a reflux outlet 25 is branched at a position ahead of the liquid delivery port 51 b of the casing 1C. One end of a reflux pipe 26 is connected so as to be communicated with this reflux outlet 25 via an adaptor 26 a, and the other end of the reflux pipe 26 is connected so as to be communicated with a reflux inlet 27 opening at the center of the bearing hole section 54 a of the rear end plate 54 via an adaptor 26 b.

As in the front and rear bearing sections 8 fA and 8 rA of the magnet pump P1 in accordance with the first embodiment, each of the front and rear bearing sections 8 fC and 8 rC comprises three sliding contact members, that is, a bushing 86 engaged with the bearing hole section 52 b inside the boss section 52 a of the partition plate 52 serving as the stationary side and the bearing hole section 54 a of the rear end plate 54 via an engagement pin 17 c so as not to be rotatable mutually, a sleeve 87 fitted over the impeller shaft 5C serving as the rotating side via an engagement key 5 f so as not to be rotatable mutually, and a thrust ring 88. Furthermore, the sleeve 87 is disposed inside the bushing 86, and the thrust ring 88 is fitted into the ring-shaped concave section of a flange section 56 provided on the impeller shaft 5C so as to make sliding contact with the end face of the bushing 86. The sliding contact members (86 to 88) of the rear bearing section 8 rC are held between the flange section 56 on the rear side of the impeller shaft 5C and a nut 57 screwed to the rear end section of the impeller shaft 5C.

Like the sliding contact members (81 to 83) of each of the bearing sections 8 fA and 8 rA in accordance with the first embodiment, the three sliding contact members, that is, the bushing 86, the sleeve 87 and the thrust ring 88, of each of these bearing sections 8 fC and 8 rC are molded products made of ceramic, such as silicon carbide (SiC), or cemented carbide, such as tungsten carbide (WC), the entire surface of each being coated with a DLC film. Furthermore, like the bushings 81 and 84 in accordance with the first and second embodiments, the bushing 86 has multiple liquid-flowing grooves 86 a formed on the inner circumferential face thereof and extending in the axial direction so as to be equally distributed. Moreover, multiple liquid-flowing grooves 86 b, extending in the radial direction and connected to the respective liquid-flowing grooves 86 a, are also formed on the end face of the outside thereof so as to be equally distributed (see FIG. 3).

In addition, a liquid reservoir section 28 is formed between the bearing hole section 54 a of the rear end plate 54 and the nut 57, and the ring-shaped sliding contact portion between the inner circumference of the bushing 86 and the outer circumference of the sleeve 87 in the rear bearing section 8 rC faces the liquid reservoir section 28 on the rear end side. Furthermore, in the front bearing section 8 fC, a liquid-flowing clearance 29 is formed between the shaft-passing hole 52 c of the partition plate 52 and the impeller 7C, and the ring-shaped sliding contact portion between the inner circumference of the bushing 86 and the outer circumference of the sleeve 87 faces the liquid-flowing clearance 29 on the front end side. Still further, the sliding contact portion between the bushing 86 and the sleeve 87 in each of the two bearing sections 8 fC and 8 rC faces the rotor chamber 60 on the outer circumferential side.

In this canned motor pump P3 in accordance with the third embodiment, the rotor 6C is rotated integrally with the impeller shaft 5C by virtue of a magnetic attraction force generated when electric power is supplied to the stator 4C. Hence, the working liquid to be fed is sucked through the liquid suction port 51 a and pressure-fed from the liquid delivery port 51 b to a target region by virtue of the centrifugal pump action owing to the rotation of the impeller 7C integrated with the impeller shaft 5C.

In the normal operation state of this canned motor pump P3, both the pump chamber 50 and the rotor chamber 60 are entirely filled with the working liquid. Since the pressure on the liquid delivery port 51 b is higher than the pressure inside the rotor chamber 60 as the pump is operated, part of the working liquid flowing toward the liquid delivery port 51 b passes from the reflux outlet 25 through the reflux pipe 26, flows into the liquid reservoir section 28 from the reflux inlet of the rear end plate 54, penetrates into the liquid-flowing grooves 86 a, of the bushing 86 in the rear bearing section 8 rC, is distributed to the sliding contact portion between the bushing 86 and the sleeve 87, then penetrates into the liquid-flowing grooves 86 b of the bushing 86, and is distributed to the entire sliding contact portion between the bushing 86 and the thrust ring 88, enters the rear side space of the pump chamber 60, and enters the front side space of the pump chamber 60 through the small clearance 9 e. In addition to the inflow of the liquid from the rear side space, the working liquid also enters the front side space of the pump chamber 60 from the through holes 24, of the partition plate 52, and this working liquid penetrates into the liquid-flowing grooves 86 b of the bushing 86 in the front bearing section 8 fC, is distributed to the entire sliding contact portion between the bushing 86 and the thrust ring 88, then penetrates into the liquid-flowing grooves 86 a of the bushing 86, is distributed to the sliding contact portion between the bushing 86 and the sleeve 87, further passes through the liquid-flowing clearance 29, and returns to the pump chamber 50. Hence, in both the bearing sections 8 fC and 8 rC, the sliding contact members (86 to 88) make sliding contact with one another while the working liquid is interposed. The lubricating action of the interposed liquid prevents breakage of the sliding contact members (86 to 88) and suppresses abrasion of the sliding contact members. Furthermore, the temperature rise owing to heat generation due to the friction at the sliding contact portions and owing to heat generation in the motor is avoided by the cooling action obtained by heat exchange with the working liquid.

On the other hand, even in the case where the pump falls into a dry operation state wherein the pump is operated while no liquid is fully distributed to the pump chamber 50 and the rotor chamber 60 because of negligence in not supplying priming water at the start of liquid feeding or because of an operating error, such as negligence in not checking the liquid level inside the pump when liquid feeding is resumed after operation interruption, or in the case where the working liquid becomes a gas-liquid mixture state owing to improper air venting in the previous stage or because of air bubbles generated from the liquid, since the surfaces of the sliding contact members (86 to 88) are coated with a DLC film being extremely hard and having a very low friction coefficient and since the adhesion strength of the DLC film to the ceramic or cemented carbide material serving as the base is excellent, as in the first and second embodiments, the sliding torque at the sliding contact face therebetween is reduced to a small value. Hence, breakage owing to load impact is prevented, and abrasion hardly occurs. Liquid feeding can thus be carried out without problems by resuming normal operation after the detection of an abnormality. Furthermore, even if the liquid is supplied without allowing a sufficient time after dry operation, film separation and cracks owing to heat shock do not occur.

In the canned pump in accordance with the present invention, the entire surfaces of the sliding contact members of the bearing sections are coated with the DLC film as described in the first to third embodiments. However, the entire surfaces are not necessarily coated with the DLC film, but the sliding contact faces thereof should only be coated with the DLC film. Furthermore, in the case where multiple kinds of sliding contact members are interposed in each bearing section, it is ideal that the sliding contact faces of all the sliding contact members are coated with the DLC film. However, the present invention includes a configuration wherein sliding contact members coated with the DLC film on the sliding contact faces thereof are combined with sliding contact members not coated with the DLC film on the sliding contact faces thereof. Moreover, the detailed configurations of the present invention, such as the structure of the casing, the installation structure of the can, the shape of the impeller, the connection structure between the impeller and the rotor, the kinds, combinations and holding structures of the sliding contact members interposed in the bearing sections, and liquid-flowing passage configurations for distributing the working liquid to the sliding contact portions of the bearing sections, can be changed variously in design so as to have configurations other than those of the embodiments.

Various methods have been known as means for forming the DLC film on the sliding contact faces of the sliding contact members of the bearing sections. The plasma ion implantation method (Nonpatent Documents 1 and 2) is suited in consideration of film formation performance, adhesion strength, etc., for three-dimensional surface portions (non-planar portions), such as the inner circumferential face of the bushing and the outer circumferential face of the sleeve. In other words, in this plasma ion implantation method, negative high-voltage pulses are applied to the base material dipped in plasma, and ions (carbon ions in the case of forming the DLC film) are accelerated and implanted in a sheath electric field formed on the surface of the base material. Since ion sheathes are formed along the surface of the base material, ion implantation can be carried out uniformly to three-dimensional surface portions. Furthermore, since ions are directly delivered from the plasma around the base material, a large beam current is obtained, and high-density ion implantation can be carried out in a short time. Still further, the method is advantageous in that low-temperature processing is possible by controlling plasma and that the apparatus for the method is relatively simple in configuration and can be produced at low cost.

[Nonpatent Document 1] J. R. Conrad, L. A. Dodd, F. G. Worzarz and N. C. Tran: Plasma source ion-implantation technique for surface modification of materials, J. Appl. Phys. 62 p 4591-4596 (1987)

[Nonpatent Document 2] Ed. By A. Anders: Handbook of Plasma Immersion Ion Implantation and Deposition, John Wiley & Sons, INC. (2000)

In addition, among these plasma ion implantation methods, the radio-frequency (RF) high-voltage pulse superimposition system (Patent Document 5 or the like) can form DLC films being thick and excellent in uniformity and adhesion strength, and is thus particularly recommended as DLC film forming means for the sliding contact members being used for the bearing sections of the canned pump in accordance with the present invention. In this radio-frequency high-voltage pulse superimposition system, as shown in FIG. 6, for example, the inside of a vacuum vessel B, in which an object M to be processed is disposed, is vacuumed via an exhaust pipe O, a plasma forming gas is introduced from a gas supply pipe I into the vacuum vessel B, a pulse radio-frequency power supply S1 for plasma generation and a high-voltage pulse power supply S2 for ion implantation are superimposed (the power supplies are mutually united while preventing mutual induction interference) using a superimposition matching circuit C, and this superimposed power is applied to the object M to be processed via a conductor L. Hence, a plasma P is generated around the object M to be processed, and the ions in this plasma P are induced and implanted to the object M to be processed using negative high-voltage pulses, and film formation is carried out while ion implantation is performed during the deposition of the radial species of the ions. Letter F in the figure designates a field-through interposed in the conductor insertion section of the vacuum vessel B to insulate the high-voltage from the vacuum vessel B.

[Patent Document 5] Japanese Published Unexamined Patent Application 2001-26889

The DLC film obtained using this radio-frequency (RF) high-voltage pulse superimposition system is formed through three stages, that is, the surface adjustment of the plasma to the object M to be processed, ion implantation to the surface layer and film formation. As gasses to be introduced into the vacuum vessel B, argon, methane or the like, is used in the surface adjustment stage; nitrogen, methane, acetylene or the like is used in the ion implantation stage; and acetylene, propane, toluene or the like is used in the film formation stage. Hence, the thickness, hardness and the like of the DLC film can be adjusted by setting the kind and introduction flow rate of the gas to be introduced, the degree of vacuum, radio-frequency power and pulse width, implantation voltage and pulse width, delay time, the number of repetitions, etc. in each stage.

It is recommended that the thickness of the DLC film to be formed on the sliding contact faces of the sliding contact members being used for the bearing sections of the canned pump in accordance with the present invention should be set in the range of approximately 0.1 to 10 μm and that the Vickers hardness thereof should be in the range of approximately 900 to 2500 Hv. Hence, in the case where the thickness of the DLC film is too thin or the hardness thereof is too low, the sliding contact faces cannot have sufficient durability. Conversely, in the case where the thickness of the DLC film is too thick or the hardness thereof is too high, the improvement in durability is slight although the cost for film formation is high, whereby the film formation is not economical. The radio-frequency acceleration voltage and the ion implantation voltage in the case of forming the DLC film having the above-mentioned thickness and hardness ranges should be in the range of 1 to 30 kV.

On the other hand, hard ceramic materials, such as silicon carbide (SiC), alumina (Al₂O₃) and silicon nitride (Si₂N₄), and cemented carbide materials, such as tungsten carbide (WC), can be used as the materials of the sliding contact members. Since silicon carbide and tungsten carbide, in particular, include carbon in the composition thereof, they have a high affinity for the DLC film, whereby they are advantageous in that they are more excellent in the adhesion strength to the DLC film than the other materials, such as alumina and silicon nitride. However, since the cemented carbide materials, such as tungsten carbide, have toughness, they are more excellent in performance than the ceramic materials, but they are expensive and difficult to be formed into complicated shapes. Hence, the cemented carbide materials are recommended so as to be used for the sleeve among the above-mentioned three kinds of sliding contact members. The static friction coefficient of the sliding contact member made of silicon carbide (standard SiC) is reduced to approximately ¼ in the case where its surface is coated with the DLC film.

The DLC film can be formed on the surfaces of metals including stainless steel without problems. However, in the case where the sliding contact members coated with the DLC film on the metal surfaces thereof are used in the bearing sections of a canned pump, and if a dry operation state or a gas-liquid mixture state of the working liquid occurs, the DLC film is apt to be cracked or separated easily since the adhesion strength of the DLC film to the metals is less than the adhesion strength of the DLC film to the ceramic and cemented carbide materials, whereby the durability becomes insufficient.

[Performance Test 1 in Dry Operation]

In the case of a large magnet pump configured as shown in FIG. 1 and FIG. 2 and having a maximum discharge of 1,100 L/min, a pump in accordance with the present invention was used in which the three kinds of sliding contact members, that is, the bushing 81, the sleeve 82 and the thrust ring 83, of each of the front and rear bearing sections 8 fA and 8 rA were molded products made of the standard SiC, and their surfaces were coated with a DLC film having a thickness of approximately 2 μm and a Vickers hardness of 1600 HV using the plasma ion implantation method conforming to the radio-frequency high-voltage pulse superimposition system. Furthermore, a pump having the conventional configuration was also used in which the sliding contact members were molded products made of the standard SiC and having no DLC film. These pumps were subjected to dry operation without supplying working liquid at a rotation speed of 3600 rpm (at a circumferential velocity of approximately 6 m/min and a bearing load of approximately 3.7 kgf at the sleeve 82).

As a result, the pump having the conventional configuration and comprising the sliding contact members having no DLC film generated abnormal sounds two seconds after the start of operation and stopped, and fell into a state of being unable to be rotated by hand. When the inside of this stopped pump was examined, the bushing 81 and the sleeve 82 of the front bearing section 8 fA and the bushing 81 of the rear bearing section 8 rA were broken. On the other hand, in the case of the pump in accordance with the present invention comprising the sliding contact members having the DLC film, the operation of the pump was stopped by switch operation 80 seconds after the start of operation. During this period, no abnormal sounds were generated. When the inside of the pump was examined after the stop of operation, all the sliding contact members of the front and rear bearing sections were normal and were not worn. The reason why this pump was stopped 80 seconds after the start of operation was to avoid the temperature of the can 2A from rising high owing to continuous dry operation for a long time.

[Measurement of Dry Static Friction Coefficient]

The sleeve 82 having the DLC film and used for the pump in accordance with the present invention and the sleeve having no DLC film used for the pump having the conventional configuration, used in the above-mentioned performance test 1, were measured in terms of dry static friction coefficient. As a result, although the dry static friction coefficient of the latter was 0.391, the dry static friction coefficient of the former was 0.099, approximately ¼. It is thus found that the surface of the DLC film has very low friction in comparison with the surface of the sleeve made of SiC.

[Performance Test in Gas-Liquid Mixture Operation]

By using a pump in accordance with the present invention having a configuration similar to that used in Performance test 1 in dry operation and a pump having the conventional configuration, and by using a working liquid in a gas-liquid mixture state wherein air was mixed in tap water at a volume ratio of approximately 50%, gas-liquid mixture operation was carried out for 15 minutes at a rotation speed of 3600 rpm (at a circumferential velocity of approximately 6 m/min and a bearing load of approximately 3.7 kgf at the sleeve 82). When the inside of each pump was examined after this operation, the bushing 81 and the sleeve 82 of the rear bearing section 8 rA in the pump having the conventional configuration were worn. However, all three kinds of sliding contact members (81 to 83) of each of the bearing sections 8 fA and 8 rA in the pump in accordance with the present invention were normal and maintained in excellent conditions similar to those before the test. The reason why the operation time was set at 15 minutes was to avoid the temperature of the can 2A from rising high, similarly as described above.

[Performance Test 2 in Dry Operation]

In the case of a small magnet pump configured as shown in FIG. 1 and FIG. 2 and having a maximum discharge of 100 L/min, a pump in accordance with the present invention was used in which the three kinds of sliding contact members, that is, the bushing 81, the sleeve 82 and the thrust ring 83, of each of the front and rear bearing sections 8 fA and 8 rA were molded products made of the standard SiC, and their surfaces were coated with a DLC film having a thickness of approximately 2 μm and a Vickers hardness of 1600 HV using the plasma ion implantation method conforming to the radio-frequency high-voltage pulse superimposition system. Furthermore, a pump having the conventional configuration was also used in which the sliding contact members were molded products made of the standard SiC and having no DLC film. These pumps were subjected to dry operation without supplying working liquid at a rotation speed of 3600 rpm (at a circumferential velocity of approximately 4.7 m/min and a bearing load of approximately 1 kgf at the sleeve 82).

As a result of the test conducted three times for the pump having the conventional configuration and comprising the sliding contact members having no DLC film, wherein the sliding contact members were replaced each time, the pump generated abnormal sounds 45 seconds after the start of operation at the first time, 2 seconds after the start of operation at the second time, and 5 seconds after the start of operation at the third time. When the inside of the pump was examined after each test, the bushing 81 and the sleeve 82 of each of the two bearing sections 8 fA and 8 rA were broken. On the other hand, the pump in accordance with the present invention comprising the sliding contact members having the DLC film was operated for 15 minutes at the first time, for 30 minutes at the second time, and for one hour at the third time, one hour and 45 minutes in total, without replacing the sliding contact members, and the pump generated no abnormal sounds. When the inside of the pump was examined immediately after the end of the third operation time, all three sliding contact members of each of the bearing sections 8 fA and 8 rA were normal, although there was a trace amount of abrasive powder attached to the liquid-flowing grooves 81 a of the bushing 81. Furthermore, when temperature measurements were carried out using heat labels, the temperature of the bushing 81 of the front bearing section 8 fA was 104° C. or less although the temperature of the bushing 81 of the rear bearing section 8 rA was raised to 166° C. or more immediately after the test, and the can 2A had a temper color indicating 200 to 250° C.

[Heat Shock Test]

By using a pump in accordance with the present invention having a configuration similar to that used for the above-mentioned Performance test 2 in dry operation, dry operation was carried out without supplying working liquid at a rotation speed of 3600 rpm (at a circumferential velocity of approximately 4.7 m/min and a bearing load of approximately 1 kgf at the sleeve 82), and room-temperature water was poured into the casing 1A at the time when one hour passed from the start of operation, whereby a test was conducted on the assumption that heat shock occurred owing to the abrupt water supply after the dry operation. Since the conditions of the one-hour dry operation are identical to those of the test operation conducted at the third time in the above-mentioned Performance test 2 in dry operation, it is assumed that the temperature of the bushing 81 of the rear bearing section 8 rA after the operation reached 1660C or more. However, after the test, all three kinds of sliding contact members (81 to 83) were free from separation and cracks and completely normal.

[Performance Test 3 in Dry Operation]

In the case of a small magnet pump configured as shown in FIG. 1 and FIG. 2 and having a maximum discharge of 100 L/min, a pump was used in which the bushing 81 and the thrust ring 83 of each of the front and rear bearing sections 8 fA and 8 rA were molded products made of the standard SiC, their surfaces were coated with a DLC film having a thickness of approximately 2 μm and a Vickers hardness of 1600 HV using the plasma ion implantation method conforming to the radio-frequency high-voltage pulse superimposition system, similarly as described above, the sleeve 82 was made of tungsten carbide serving as a base material, and its surface was coated with a similar DLC film. When dry operation was carried out without supplying working liquid at a rotation speed of 3600 rpm (at a circumferential velocity of approximately 4.7 m/min and a bearing load of approximately 1 kgf at the sleeve 82) for one hour, abnormal sounds were not generated. When the inside of the pump was examined after the stop of this operation, the three kinds of sliding contact members (81 to 83) of each of the bearing sections 8 fA and 8 rA were found to be normal, although there was a trace amount of abrasive powder attached to the liquid-flowing grooves 81 a of the bushing 81.

[Performance Test 4 in Dry Operation]

In the case of a small magnet pump configured as shown in FIG. 1 and FIG. 2 and having a maximum discharge of 100 L/min, a pump was used in which the bushing 81 of each of the front and rear bearing sections 8 fA and 8 rA was a molded product made of the standard SiC, its surface was coated with a DLC film having a thickness of approximately 2 μm and a Vickers hardness of 1600 HV using the plasma ion implantation method conforming to the radio-frequency high-voltage pulse superimposition system, similarly as described above, the sleeve 82 and the thrust ring 83 were made of SUS316 serving as a base material, and their surfaces were coated with a similar DLC film. When dry operation was carried out without supplying working liquid at a rotation speed of 3600 rpm (at a circumferential velocity of approximately 4.7 m/min and a bearing load of approximately 1 kgf at the sleeve 82), abnormal sounds were generated 9 minutes and 25 seconds after the start of operation. Hence, the operation was stopped. When the inside of the pump was examined after this operation stop, the bushing 81 of each of the front and rear bearing sections 8 fA and 8 rA was normal. However, the DLC film on the sleeve 82 of the rear bearing section 8 rA was worn, and the surface of the base material, SUS316, was exposed at some points. Furthermore, the sleeve 82 of the front bearing section 8 fA was found worn slightly, and the abrasive powder of the DLC film accumulated at the bottom section of the driven-side space 10 b. According to this result, it is found that the sliding contact members of the bearing sections made of a metal serving as a base material, even when coated with the DLC film on their sliding contact surfaces, cannot obtain sufficient adhesion strength and abrasion resistance in comparison with the sliding contact members made of ceramic, such as silicon carbide (SiC), or cemented carbide, such as tungsten carbide, in particular, serving as a base material, and that the DLC film was damaged suddenly when an operating error, such as dry operation, occurred.

In conclusion, the canned pump of the present invention has the remarkable operations and effects as recited hereinafter. The sliding contact members interposed in the bearing sections for the impeller shaft have a DLC film on the sliding contact faces thereof. Since this DLC film is extremely hard, has a very low friction coefficient and is excellent in the adhesion strength to the base material thereof, such as ceramic or cemented carbide, the sliding torque at the sliding contact face therebetween is reduced to a small value even if a dry operation state occurs temporarily because of an operating error or the like at the start of liquid feeding or at the time when liquid feeding is resumed after operation interruption. Hence, breakage owing to load impact is prevented, and abrasion hardly occurs. Furthermore, even if the sliding contact members having been heated by frictional heat generation are quickly chilled by supplying liquid without allowing a sufficient time after dry operation, separation and cracks owing to heat shock do not occur, whereby subsequent liquid feeding can be carried out in a proper state. On the other hand, even in the case where the working liquid becomes a gas-liquid mixture state owing to improper air venting in the previous stage or because of air bubbles generated from the liquid, the sliding contact members are not broken and are suppressed from being worn, and normal operation can be resumed thereafter, and liquid feeding can be carried out without problems.

With the invention in accordance with Claim 2, the sliding contact member having the DLC film is at least one selected from the bushing fitted into the bearing hole section, the sleeve fitted over the impeller shaft, and the thrust ring making contact with the end face of the bushing and/or the sleeve, whereby the resistance of the bearing sections against a temporary dry operation state can be ensured and abrasion can be prevented, and abrasion of the bearing sections in a gas-liquid mixture state can be suppressed. Hence, it is a matter of course that the most satisfactory results can be obtained, provided that all of these sliding contact members have the DLC film.

With the invention in accordance with Claim 3, the sliding contact faces of the sliding contact members have the liquid-flowing grooves. Hence, the liquid is reliably distributed to the entire sliding contact faces through the liquid-flowing grooves, and friction is lowered.

With the invention in accordance with Claim 4, the sliding contact members having the DLC film are made of a material including carbon, such as silicon carbide or tungsten carbide. Hence, the DLC film has high adhesion strength to the material on the basis of its high affinity, and DLC film boundary separation and cracks are prevented even if a large load impact is applied owing to dry operation or the like.

With the invention in accordance with Claim 5, the thickness of the DLC film on the sliding contact face of the sliding contact member has a specific range, and with the invention in accordance with Claim 6, the hardness of the sliding contact face having the DLC film has a specific range. Hence, the sliding contact member can have sufficient abrasion resistance and strength, and the cost for forming the DLC film can be reduced.

With the invention in accordance with Claim 7, the DLC film is formed using the plasma ion implantation method. Hence, the DLC film can be formed securely on the three-dimensional surfaces of the sliding contact members in a short time at low cost using an apparatus having a simple configuration. Furthermore, with the invention in accordance with Claim 8, the plasma ion implantation method conforms to the radio-frequency high-voltage pulse superimposition system. Hence, the DLC film can be made uniform and thick.

With the invention in accordance with Claim 9, the canned pump is provided as a canned magnetic coupling type magnet pump in particular, and with the invention in accordance with Claim 10, the canned pump is provided as a canned motor pump in particular, wherein the sliding torque at the sliding contact face is reduced to a small value even if a dry operation state occurs temporarily. Hence, breakage owing to load impact is prevented, and abrasion hardly occurs, and separation and cracks do not occur even if the sliding contact members are quickly chilled by supplying liquid after dry operation. Furthermore, even if the working liquid falls into a gas-liquid mixture state, breakage of the sliding contact members is prevented and abrasion is suppressed. 

1. A canned pump in which drive magnetic force generating means disposed outside a can having a bottom, the can being hermetically sealed from an outside and an inside of the can being communicated with an inside of the pump, whereas a rotor concentrically fitted over an impeller shaft is disposed inside the can, and the rotor is rotated integrally with an impeller around the impeller shaft by virtue of magnetic action generated between the drive magnetic force generating means and the rotor, characterized in that a sliding contact member made of ceramic or cemented carbide and having a diamond-like carbon film on a sliding contact face thereof is interposed in a bearing section for the impeller shaft.
 2. A canned pump in accordance with claim 1, wherein the sliding contact member having the diamond-like carbon film is at least one selected from a bushing fitted into a bearing hole section, a sleeve fitted over the impeller shaft, and a thrust ring making contact with an end face of the bushing and/or the sleeve.
 3. A canned pump in accordance with claim 1, wherein liquid-flowing grooves are formed on the sliding contact face of the sliding contact member.
 4. A canned pump in accordance with claim 1, wherein the sliding contact member having the diamond-like carbon film is made of silicon carbide or tungsten carbide.
 5. A canned pump in accordance with claim 1, wherein a thickness of the diamond-like carbon film is in the range of about 0.1 to about 10 μm.
 6. A canned pump in accordance with claim 1, wherein a Vickers hardness of the sliding contact face having the diamond-like carbon film is in the range of about 900 to about 2500 Hv.
 7. A canned pump in accordance with claim 1, wherein the diamond-like carbon film is formed using a plasma ion implantation method.
 8. A canned pump in accordance with claim 7, wherein the plasma ion implantation method conforms to a radio-frequency high-voltage pulse superimposition system wherein a pulse radio-frequency power supply for pulse plasma generation and a negative high-voltage pulse power supply for ion implantation are superimposed to generate a plasma around a base material and to induce ions inside the plasma into the base material using high-voltage pulses.
 9. A canned pump in accordance with claim 1, wherein the drive magnetic force generating means is a cylinder integrated with a drive shaft and provided with a drive magnet on an inner circumferential side thereof, and a driven magnet is provided on an outer circumferential side of the rotor.
 10. A canned pump in accordance with claim 1, wherein the canned pump is a canned motor pump, the drive magnetic force generating means of which is a stator of a motor. 